Molybdenum disulfide is a well-known lubricant additive. Because it is insoluble in lubricating oils, however, oil soluble sulfur containing molybdenum compounds have been proposed and investigated as lubricant additives. For example, in U.S. Pat. No. 2,951,040, an oil soluble molybdenum xanthate is disclosed as being useful in lubricating compositions. Apparently, the molybdic xanthate decomposes under conditions of use to form an oil insoluble solid molybdenum sulfide on the metal surfaces being lubricated.
U.S. Pat. No. 3,419,589 discloses the use of certain "sulfurized" molybdenum (IV) dialkyldithiocarbamates as lubricant additives. These additives are described as being oil soluble or at least capable of being easily suspended in oils.
U.S. Pat. No. 3,840,463 discloses the use of certain metal dialkyldithiocarbamates or dithiophosphates in combination with metal-free additives containing sulfur and phosphorus.
U.S. Pat. No. 4,588,829 discloses the use of (disulfido) tris (N, N-substituted dithiocarbamato) Mo(V) complexes in lubricant compositions.
In copending application Ser. No. 404,142, filed Sept. 7, 1989, there is disclosed a multifunctional additive formed by reacting molybdenum hexacarbonyl with dixanthogens of the formula (ROCS.sub.2).sub.2 wherein R is an organo group having a sufficient number of carbon atoms to render the additive soluble in a base lubricating oil.